Ultracentrifuge



Aug. 27, 1940. J. w. McBAlN 2,213,107

ULTRACENTRIFUGE Filed Nov. 2 1938 2 Sheejs-Sheet 1 27, 1 0. J. w. MOBMN 2,213,101

ULTRACEN TR IFUGE Filed Nov. 28, 1938 2 Sheets-Sheet 2 Patented Aug. 27, 1940 ULTRACENTRIFUGE James w. McBain, Palo Alto, Calii., assignor to Research Corporation, New York, N. ,Y., a corporation of New York Application November is, 1938, Serial No. 242,851

10 Claims.

This invention relates to apparatus for subjecting materials having a fluidconstituent to very great force for the purpose of bringing about sedimentation within the material whereby separation of constituents of the material may be effected and the sedimentation characteristics of the constituents may be studied. with what have become known as ultracentrifuges. An ultracentrifuge is characterized by 10 the very great centrifugal force it exerts in steady manner and in the absence of .convection currents in the material undergoing centrifugation. If uniform settling is to be obtained, and this is necessary if cleancut separations are to be made and sedimentation phenomena are to be accurately measured, the centrifuge must rotate at constant speed, quite free of vibration, and at constant temperature. It is important that the individual particles be free to diffuse, free to carry out Brownian movement, and free to sediment radially inwards or outwards, but it is equally important that the liquid as such be immobilized and free. from convection currents.

In the present invention constant speed and temperature are realized by supporting the rotor of the centrifuge while it is spinning on a slip stream of air released from nozzles at constant pressure and temperature. Vibration may be sup-.

pressed by contacting the stator of the centrifuge with a piece of soft sponge rubber. The restraint on the liquid is provided by spacing parallel plates very close together so that the frictional forces exerted due to the'surfaces of the plates are large relative to ordinary forces causing convection such as vibration, slight temperature diiier ences, and the like.

The invention includes a high speed centrifugal rotor assembly comprising means providing a chamber and a plurality of substantially flat radially extending plate members occupying a portion of said chamber and providing therebetween a plurality of radially extending passages having axial dimensions so small as to substantiallyimmobilize the fluid contained in the passages while maintaining said fluid subject to substantially the full centrifugal force within the rotor.,

A principal object of the invention is to provide in a high speed centrifuge means which 5 permit unobstructed movement of separate particles or molecules in a sample undergoing centrifugation while maintaining the bulk of the liquid sample relativelyimmobile.

An important object of the invention is to provide means for maintaining the sample which It has to do has been centrifuged immobile even after thecentrifuge has stopped revolving, thus permitting the removal of separate portions of the sample.

Another object of the invention is to provide a rotor for a centrifuge which will permit the removal of portions of the sample at selected intervals or after equilibrium has been reached while the centrifuge rotor is revolving.

A further object of the invention is to provide an ultracentrifuge with an opaque rotor that permits studies in sedimentation phenomena without an optical system.

Another object of the invention is to-supply a simple, inexpensive centrifuge which will provide accurate determinations of rates of sedimentation and sedimentation equilibrium when operated by workers who have average skill in using apparatus of this general type. The manner in which the above mentioned and other objects are realized will be pointed out in the following detailed description of the invention with reference to the drawings in which:

Fig. 1 illustrates the several elements in separated arrangement, shown in partial medial section, which comprise the rotor chamber of the preferred form of the invention;

Fig. 2 is a planview of a preferred form of insert for immobilizing the liquid centrifuged in the chamber shown in Fig. 1;

Fig. 3 is a vertical section of the insert shown in Fig. 2 taken along the line 33 of that figure;

Fig.4 is a plan view of another form of insert for use in the chamber shown in Fig. 1;

Fig. 5 is a vertical section of the insert taken along the line 55 of Fig. 4;

Fig. 6 is a vertical medial section of a stack of elements which, assembled as shown, has been satisfactorily used as an immobilizing insert in accordance with the invention, the broken lines indicating the position of a centrifugal chamber containing the elements;

Fig. 7 is a sectional elevation, taken along the line 'i-i of Fig. 8, of an immobilizing arrangement of somewhat different construction posi tioned in a suitable chamber for the same in accordance with the teachings of this invention, the conical cover being indicated in broken lines;

Fig. 8 is a bottom plan view of the arrangement of Fig. 7 not showing the conical cover;

Fig. 9 is a sectional plan view, taken along the line 9-9 of Fig. 10, of another embodiment of the invention;

.Fig. 10 is a vertical medial section of the apparatus shown in Fig.- 9 on the line ill-l0 of Fi 9;

Fig. 11 is a detail in section of the bottom element of a stack of immobilizing elements as shown in Fig. 10;

Fig. 12 1s a plan view of two layers of immobilizing elements for use in the chamber shown in Figs. 9 and 10;

Fig. 13 is a medial sectional elevation of a stack of elements like those shown in Fig. 12;

Fig. 14 is a vertical medial section of a stator for causing rotation of the several rotors illustrated in several of the other figures, indicating in broken lines the position of a rotor at rest; and

Fig. 15 is an alternative form of stator shown in vertical medial section.

The centrifuge chamber comprising the elements shown in Fig. 1 is correctly positioned in that figure for filling and assembly, but after assembly the apparatus is turned upside down and rotated with the cone at the bottom. It comprises a-cup 30 with top edge threaded as indicated at 3|, a conically shaped cover 32 provided with female threads to screw over the threads on member 30. Cup 30 is made strong enough to withstand the strains set up when the apparatus is revolving but there is sufficient flexibility in the threaded wall to permit it to expand under the centrifugal force exerted during rotation and press into the threads in cover 32. This temporary expansion keeps the parts together securely even though the initial screwing together of the parts was done with relatively slight pressure. Cover 32 is ruggedly constructed, the metal at the greatest diameter, at curved portion 36, extending out to furnish the strength necessary to withstand the breaking strains of cover 32 itself and the added strains set up by part 30. A threaded recess 3'! is provided to take a threaded holding tool (not shown) which is useful in assembling the centrifuge. A band wrench is efiective in holding cup 30. Alternatively, the holding tool may be provided with a handle and serveas a wrench while part 30 is held in a split holder clamped in a vise.

The rotor cup is turned from materials of high tensile strength not corroded by the materials to be tested; as examples. stainless steel or alloy steels, which may be coated with Bakelite lacquer baked on after the parts are fabricated and finished, may be used. Monel metal and coin silver can be used advantageously. In rotors having outside diameters not exceeding about 37 mm. walls from 2 to 2 mm. thick have been found sufficiently strong for speeds of from 2,000 to 3,000 revolutions per second. The cone of the rotor is preferably formed with an angle of 100 degrees between diametrically opposed slant heights. The conical depression or cup in the stator to rotate such rotor preferably has an angle of about 90 degrees.

An insert indicated by C in Fig. 1, is placed in the chamber 30 with the sample before it is closed by conically shaped cover 32. The insert assembly indicated at C and illustrated in Figs. 2 and 3 is made up of a disc 40 to which a rivet 4| is attached, alternate wide washers 42 and narrow washers 43 piled upon rivet 4| and a second disc '40 fastened to and held by rivet 4| after the washers are assembled. The washers are flat, about .076 mm. in thickness and an assembly usually comprises 50 or more of each diameter. Assembly C fits rather snugly into cup 30 and two small holes 45, or alternatively square notches, are made in bottom disc 40 and two similar holes or notches 45' are provided in top disc 40 to permit removal of samples or introduction of material and facilitate introduction and removal of the assembly itself. 1: the assembly is to be taken apart, a screw can replace rivet 4|.

The washers comprising assembly C have been described-as being .076 mm. (.003 inch) in thickness and spaced .076 mm. apart, which is a suitable axial dimension of the radially disposed immobilizing members when aqueous liquids are treated. However, satisfactory results have been obtained with various liquid media when using immobilizing elements of varied thickness spaced apart to provide cells or passages having axial dimensions of the order of .001 to .01 inch. Such cells or passages have been found to provide the desired frictional constraint for the various media subjected to centrifugal force in ultracentrifuges provided with the immobilizing inserts of this invention.

The centrifuge shown in Fig. 1, with the insert shown in Figs. 2 and 3 is assembled and used as follows. The sample to be studied and assembly C are placed in a sausage casing or other impervious flexible container and the container is placed in a small commercial centrifuge. The centrifuge is rotated for a minute or so which causes all the air in assembly C to be driven out and replaced by the material to be studied. The commercial centrifuge is stopped and assembly C is removed and placed in cup 30. It continues to hold, because of capillary or frictional forces, the material of the sample. Now an additional portion of the sample is injected into one of the holes 45' and the space between the outer edges of washers 42 and the wall of cup 30 is filled to disc 40'. A thin disc of suitable plastic material 33 is placed over the top of disc 40' and the top edge -of cup 30. Over disc 33 is placed a semi-flexible disc 34 of metal and upon top of disc 34 is a thin metal washer 35. Washer 35 affords relative motion while cover 32 is being screwed on, either between disc 34 and washer 35 or between cover 32 and washer 35 or at both sets of contacting surfaces. The assembled rotor with sample is now turned over, placed upon a stator such as that shown in Figs. 14 or 15 and caused to rotate. After a definite period of rotation the rotor is stopped, the cover is removed and a measured sample is removed through one of the top holes 45. The outer material, of which the withdrawn sample is a portion, had been free to undergo convection during the centrifuging and the sample is, therefore, uniform. The increase of concentration measures the amount of dissolved or suspended molecules or particles which have moved outwards from the liquid within the washer assembly C. Likewise the loss of molecules or particles from the immobilized liquid may be studied by throwing out the immobilized liquid into a cup empty of liquid at the periphery.

Figs. 4 and 5 show an alternate insert for use in the chamber shown in Fig. l for immobilizing the liquid centrifuged in. that chamber. It is made up of nested groups of washers 46, 41 and 48, each group being held together loosely with rivets 50. The rivets are long enough to permit slight movements of the washers on the shanks of the rivets enabling liquid to enter between the washers. The nest is placed in cup 30, the sample to be studied is placed in hole 49 in the inner group of washers 48, cover 32 is screwed on, and the assembled centrifuge is turned over and rotated by operating means later to be described. Centrifugal force causes the liquid to flow between the washers where as a body it is held immobile but where molecules or particles are permitted to move inwardly or outwardly, depend-,

ing upon their relative molecular weight or bottom of holes 24 when rotation ceases, and the specific gravity. in orderly fashion. After'a'suitw able time of rotation, the centrifugeis stopped and opened and the groups of washers are separately removed. The portions of the sample held by friction or surface attraction between the several groups of washers are separately removed, say, in a small hand centrifuge, and analyzed to determine rate, equilibrium, true density and number of particle sizes. With this insert it is possible-to study also polyphase systems.

Fig. 6 shows an assembly of simple, easily arranged, and easily cleaned parts which can be used for immobilizing liquid in a centrifuge of the construction shown in Fig. 1. It can be used instead of the inserts already described in those problems where sedimentation equilibrium of mono-disperse systems is to be studied. The assembly is comprised of a pile of very thin plane horizontal annular rings or washers. The washers are all of the same outside diameter, making a neat sliding fit in the cup or bowl of the centrifuge, indicated in construction lines in Fig. 6, but are alternately narrow and wide, the narrow washers 39 serving as spacers for wide washers 38, thus producing radially extending annular spaces between which the liquid can not move by convection.

In using theinsert shown in Fig. 6, just enough liquid is placed in the centrifuge to fill the annular spaces and to supply a mobile supernatant layer lining the hole through the wide washers. The cover is put on and the rotor is spun until equilibrium has been obtained. The supernatant liquid is now of uniform concentration and is of necessity identical with that portion of the immobilized liquid with which it is in immediate contact. Hence, when the rotor is stopped and the supernatant liquid removed, for analysis by any convenient method, it is found to be less concentrated than the original solution placed in the rotor.

The rotor illustrated in Figs. 7 and 8 comprises a bowl or cup 20 similar to cup 30 in Fig. 1 except that the interior vertical wall is formed with alternate projecting portions 2| and bays 22. Alternatively, a container or cell comprising the scalloped construction of cup 20 may be inserted in cup 30. The cover, which becomes the bottom when in position for spinning, may be and usually is, member 32 shown in Fig. 1, sealing members 33, 34 and 35 being used for making a tight joint as previously described. The insert for immobilizing the liquid is merely a pile of thin fiat washers 23 all of the same outside diameter and each having a similar hole 24. The projecting portions 2| hold the washers in position symmetrically about the vertical axis of member 20. In using the rotor and insert shown in Figs. '7

and 8, the materialto be-studied is first placed in cup 20 in suflicient amount to almost fill the cup after the insert is added. If each washer of the insert has been wetted with the material, the washers may be assembled outside the cup and then introduced as a pile. But it is preferred to introduce the washers one by one, letting each one sink into the material within the cup and becomev "wetted by it before the next is added. When sufiicient washers have been placed in the cup to fill it, a thin layer of the material being held immobile between each pair of surfaces of adjacent washers and bays 20 and at least part of holes 24 being filled, the cover is screwed on and the rotor spun for what experience has shown the a suitable length r time. After spinning, thesupernatant liquid. 25, which flows to the liquid in bays 22, are separately sampled. The portions of the liquid in the bays 22 can readily undergo convection and so are average samples of the constituents that have passed outwardly between the washers and because of their specific gravity remain in the outer regions of the rotor. The liquid in holes 24 is'also an agitated average sample. These average samples 'are'in equilibrium, respectively, with the liquidand suspension just inside the outer edges of washers 23 and with the liquid (and suspension, if any), just inside the inner edges of washers 23. By. taking the two samples after equilibrium has been attained and analyzing them,'thesedimentation equilibrium of the system studied can be ascertained. r

In Figs. 9, 10, 11, 12 and 13, a rotor comprising a single piece container or cup I holds in a hollowed out space 6 an assembly of annular disc sectors 2 and a bottom perforate disc 3. The top, of the rotor is recessed at 1 to receive an imperforate top plate 4 when such top is desired. The bottom of the rotor I has grooves or flutes 8 cut in the surface so that the gas issuing from the nozzles or openings in the stator will have increased tractive effect. The hole 5 in the rotor whichgives access to cavity 6 is made large enough for easy passage of annular disc sectors 2, but of radius less than the inner radius of the annular disc sectors, so that excess liquid may be retained within the rotor.

Bottom disc 3 is made of flexible sheet material. To: place disc 3 in cavity 6 it is folded up like a partially closed umbrella, then inserted through. hole 5 and then unfolded and pressed down until it is nearly fiat as in Fig. '11. The edge of disc 3 should not contact the wall of cavity 6 so intimately that a tight joint is obtained because liquid is to pass around the outer edge of the disc as will be explained later. The sectors 2 commonly extend over about 65 degrees, permitting three sectors to be placed in a common plane degrees apart with open spaces between of 55 degrees. These spaces. when bridged by sectors in the plane above and the plane below, provide thin horizontal cells l0 in which the material being tested, as a whole, is immobile because of the friction provided by the closely spaced surfaces. Individual particles or large molecules as indicated by p and p in Fig. 9 are free to move to the degree the forces acting upon them permit and as the principal force is radially outward they move without obstruction in that direction to the wall of the rotor or until equilibrium is reached. Fig. 13 shows two layers of annular disc sectors 2 arranged as laid up in the chamber'G, showing the overlapping configuration of alternate layers. The apparatus illustrated in Figs. 9 and 10 is used as follows. Bottom disc 3 is folded and inserted into roor casing l as above described and forced down upon the bottom of cavity 6 until it is fiat as in Fig. 10, the central hole being above a slight depression 6 in the floor of the rotor cavity. The sectors 2 are now inserted one at a time and ,assembled in overlapping arrangement as shown in Figs. 9 and 10 until the cavity is filled with the sectors. An amount of the liquid or liquidsuspension' mixture just sufficient to fill the spaces or cells between the sectors is now innecessary is known from previous determinations. Alternatively, excess is introduced and the .excess then removed when spinning. If the liqtime-perhaps for some houses, the top 4 is removed while the rotor is spinning by a small flame playing upon the wax seal, or Cellophane, or cutting the seal wih the corner of a razor. Measured amounts of a heavy liquid not miscible with the material being tested (carbon tetrachloride is commonly satisfactory) is dropped through the top of the rotor, care being taken that it goes through hole l3 into depression This liquid goes under disc 3 and out to the periphery of cavity 6 where, because of its high specific gravity, it spreads upwards over the edge of disc 3 and displaces the liquid and particles in the outer regions of the cells I0. As the liquid in the cells is forced inwardly the color and other characteristics of the liquid appearing at the inner face of the cells l0, that is, at surface it, are

: noted, after or while it is being removed with a scraping pipette. When a particular constituent in which the operator is interested appears, for instance, a red color when a test is being made for hemoglobin, the amount of displacement liquid is noted. From this value the innermost position of the hemoglobin during centrifugation can be calculated and from formulae known to physical chemists the rate of sedimentation can be determined.

A brief description of the stators used for rotating the rotors at high velocity will be given for purposes of indicating their functions.

Fig. 14 comprises a simple stator which permits air at constant temperature and pressure p to enter through tube 64 into distributing channel 62 above member 60 from whence it is released through nozzles 65 in a direction at an angle to the conical surface of the stator so that it tends to rotate the rotor placed within the cone of the stator. A thin disc or plate 68, preferably of light metal such as Duralumin, is clamped between parts GI and 60 when they are brought together through tightening of threads BI and this disc is supported on a ledge 61" on the wall of a hole 61 in a table indicated by horizontal member 81. The disc is not otherwise restrained and so permits adjustment of the stator assembly when the rotor is revolving and also absorbs vibration which may be set up by the air flow and revolving member. More effective adjustment and dampening of vibration can be obtained when necessary by inserting pieces of sponge rubber (not shown) between member 68 and ledge 61". The stator cone 6| may be provided with a metal ring 8|, preferably of brass, to give long wearing properties to that portion of its surface contacted by the rotor in starting and stopping. When the ring becomes worn out it may be readily replaced by a new one.

In Fig. 15 the air for rotating the cup is introduced through pipe 10 into annular space '11 which distributes it-to nozzles 15. In addition to the air supplied the stator by pipe I0, is a source of air made available through tube H which is slipped over inlet tube 12. The air entering through tube H, and adjusted as to quantity and pressure through clamp 13, is for the purpose of giving an additional cushion effect to the rotor revolving in the cup defined by number 14. An annulus of sponge rubber 16 preferably is placed between the table 61 and the disc 68 to damp vibration set up in the stator. Positioning members, for example, screw 69, hold the assembly loosely in a more or less definite position while leaving rubber member 16 free of restraint to provide the desired cushioning effect. It is desirable to place a stationary protective guard (not shown) about the rotor to insure protection to those operating the apparatus.

The position of a rotor at rest is indicated by dotted lines in Fig. 14. When the air is turned on, the rotor rises and is supported on a vertically rising stream of air, which at the same time causes the rotor to spin due to the tangential component of force given the air stream by the inclined nozzles. The conical surface of the rotor may be fluted or grooved, as shown at 80 in Fig. 1, to give increased traction between the rotor and the air stream.

The stator shown in Fig. 14 is usually satisfactory for spinning the rotors, but with some forms of rotors the stator shown in Fig. 15 has been found more satisfactory in permitting exact adjustment of the position of the rotor while spinning, so that with some rotors the speed with a given air pressure is increased by about ten per cent.

The term "immobilize as used in the specification and claims denotes that the body of fluid contained in the passages between the immobilizing plates is maintained substantially free from convection currents when the centrifuge is rotating at substantially constant velocity, without interfering with relative movement between the components of the fluid such as sedimentation, Brownian movement and the like, and without interfering with radial displacement of the fluid in bulk when desired, for example, by adding fluid to or removing fluid from the chamber of the centrifuge while the rotor is in motion.

I claim:

1. A high speed centrifugal rotor assembly comprising means providing a chamber adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of the chamber and a plurality of substantially flat radially extending plate members occupying a portion of said chamber and providing therebetween a plurality of radially extending passages having axial dimensions of the order of .001 to .01 inch, whereby at least a portion of the fluid contained in said chamber is substantially immobilized and subject to substantially the full centrifugal force within the rotor.

2. A high speed centrifugal rotor assembly comprising means providing a chamber adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of the chamber and a plurality of substantially flat radially extending plate members occupying a portion of said chamber and providing therebetween a plurality of radially extending passages unobstructed in the radial direction and having axial dimensions of the order of .001 to .01 inch, whereby at least a portion of the fluid contained in said chamber is substantially immobilized and subject to substantially the full centrifugal force within the rotor.

3. A high speed centrifugal rotor assembly comprising means providing a chamber adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of the chamber and a plurality of substantially flat radially extending plate members occupying a portion of said chamber and providing therebetween a plurality of radially extending passages having axial dimensions of the order of .001 to .01 inch, whereby fluid contained in said radially extending passages is substantially immobilized and subject to substantially the full centrifugal force within the rotor.

4. A high speed centrifugal rotor assembly comprising mans providing a chamber adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force byrotation of the chamber and a plurality of substantially flat radially extending plate members occupying a portion of said chamber and providing therebetween a plurality of radially extending passages unobstructed in the radial direction and havin axial dimensions of the order of .001 to .01 inch, whereby fluid contained in said radially extending passages is substantially immobilized and subject to substantially the full centrifugal force within the rotor.

5. A high speed centrifugal rotor assembly comprising a bowl member providing a chamber symmetrical about the axis of rotation of said rotor, said chamber being adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of said bowl member, means coaxial of said rotor occupying and filling the central portion of the chamber, and a plurality of annular discs engaging at their inner peripheries the surface of said filling means and extending radially outwards therefrom, consecutive discs being separated in an axial direction a distance of the order of .001 to .01 inch and providing therebetween a plurality of radially extending passages unobstructed in the radial direction, whereby fluid contained in said radially extending passages is substantially immobilized and subject to substantally the full centrifugal force of the rotor in the radial direction.

6. A high speed centrifugal rotor assembly comprising a bowl member providing a chamber symmetrical about the axis of rotation of said rotor, said chamber being adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of said bowl member and a stack of annular discs occupyin a portion of said chamber, engaging the vertical wall thereof, and providing a well coaxial of the chamber, said discs being separated in an axial direction a distance of the order of .001 to .01 inch and providing therebetween a plurality of radially extending passages whereby fluid contained in said radially extending passages is substantially immobilized and subject to substantially the full centrifugal force of the rotor in the radial direc- 7. A high speed centrifugal rotor assembly comprising a bowl member providing a chamber symmetrical about the axis of rotation of said rotor, said chamber being adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of said bowl member and a plurality of radially extending annular discs occupying a portion of said chamber, said discs being arranged within said chamber in a plurality of separable coaxial cylindrical stacks, the outermost stack engaging the vertical wall of the chamber, and the innermost stack providing a well coaxial of the chamber, the discs in any one stack being separated in an axial direction a distance of the order of .001 to .01 inch and providing therebetween a plurality of radially extending passages whereby fluid contained in said radially extending. passages is substantially immobilized and subject to substantially the full centrifugal force of the rotor in the radial direction.

8. A high speed centrifugal rotor assembly comprising a bowl member providing a chamber symmetrical about the axis of. rotation of said rotor, said chamber being adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of said bowl member and a stack of radially extending annular discs occupying a portion of said chamber, engaging the vertical wall thereof and providing a well coaxial of the chamber, alternate annular discs of said stack having a thickness of the order of .001 to .01: inch and having their inner radii of greater magnitude than the inner radii of the remaining discs, whereby to maintain said remaining discs separated in an axial direction a distance of the order of .001 to .01 inch and providing between said remaining discs a plurality of radially extending passages whereby fluid contained in said radially extending passages is substantially immobilized and subject to substantially the full centrifugal force of the rotor in the radial direction.

9. A high speed centrifugal rotor assembly comprising a bowl member pzoviding a chamber symmetrical about the axis of rotation of saidv rotor, said chamber being adapted to hold a body of fluid while subjecting said fluid to centrifugal force by rotation of said bowl member, means coaxial of said rotor occupying and filling the central portion of the chamber, and a plurality of annular discs engaging said filling means at their inner peripheriesand extending radially outward therefrom, alternate annular discs having a thickness of the order of .001 to .01 inch and having the outer radii of smaller magnitude than the outer radii of the remaining discs, whereby 'to maintain said remaining discs separated in an axial direction a distance of the order of .001 to .01 inch, and providing between said remaining discs a plurality of radially ezrtending passages, whereby fluid contained in said radially extending passages is substantially immobilized and subject to substantially the full centrifugal force of the rotor in the radial direction.

10. A high speed centrifugal rotor assembly comprising means providing a chamber adapted to hold a body of fluid while subjecting said body of fluid to centrifugal force by rotation of the chamber, a plurality of radially extending plates occupying a portion of said chamber and means spacing said plates apart in an axial direction to provide radially extending passages therebetween having axial dimensions of the order of .001 to .01 inch, whereby fluid contained in said radially extending passages is substantially immobilized and subject to substantially the full centrifugal force within the rotor.

' JAMES W. MGBAIN. 

